Yurok tribe member, Thomas Willson of Weitchpec, Ca. checks on his drift net that he has strung out across the Klamath River in search for Steelhead fish. He lives on the Eastern most edge of teheYurok tribal lands.Photo By Michael Macor/San Francisco Chronicle Photographed in, Klamath, Ca, on 2/12/08

Photo: Michael Macor, The Chronicle

Yurok tribe member, Thomas Willson of Weitchpec, Ca. checks on his...

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A file photo shows the Copco No. 1 dam operated by PacifCorp on the Klamath River outside Hornbrook, Calif., on March 16, 2004. Warren Buffett's MidAmerican Energy Holdings Co., which provides power for 5 million customers worldwide and is the largest utility in Iowa, is acquiring PacifiCorp, an electric utility with customers in six Western states, for $5.1 billion in cash, it was announced Tueday May 24, 2005. (AP Photo/Jeff Barnard)

Water not diverted by the J.C. Boyle Dam flows back into the Klamath River Aug. 21, 2009 near Keno, Ore. Dam owner PacifiCorp announced a tentative agreement Wednesday, Sept. 30, 2009, to remove the Boyle and three other dams it owns on the Klamath River, marking the latest milestone in efforts to restore what was once the third biggest salmon run on the West Coast.

Photo: Jeff Barnard, AP

Water not diverted by the J.C. Boyle Dam flows back into the...

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Water flows back into the Klamath River Aug. 21st outside Keno, Ore., after being diverted by J.C. Boyle Dam upstream and running through the powerhouse shown here to make electricity. PacifiCorp announced Wednesday, Sept. 30, 2009 the terms for giving up four hydroelectric dams on the Klamath so they can be removed by the government to help struggling salmon runs.

Photo: Jeff Barnard, AP

Water flows back into the Klamath River Aug. 21st outside Keno,...

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Iron Gate Dam spans the Klamath River Aug. 21, 2009 near Hornbrook, Calif. The dam is one of four that PacifiCorp has tentatively agreed to allow removed to help struggling Klamath River salmon.

Copco 2 Dam regulates outflows from Copco 1 upstream on Aug. 21, 2009 on the Klamath River near Hornbrook, Calif. PacifiCorp has tentatively agreed to allow this and three other dams to be removed from the Klamath to make way for restoration of struggling slamon runs.

Photo: Jeff Barnard, AP

Copco 2 Dam regulates outflows from Copco 1 upstream on Aug. 21,...

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Water trickles down the face of Copco 1 Dam on Aug., 21, 2009 on the Klamath River near the Oregon-California border outside Hornbrook, Calif. PacifiCorp, the owner of the 137-foot concrete arch dam, announced Wednesday, Sept. 30, 2009, terms of a tentative agreement to remove this and three other dams. It is the latest milestone in efforts to start removing the dams in 2020 to help struggling salmon runs.

In what is being touted as the world's biggest dam-removal project, an agreement was reached Tuesday to remove four dams on the Klamath River and restore a 300-mile migratory route for California's beleaguered salmon.

The tentative agreement was reached after a decade of negotiations among 28 parties, including American Indian tribes, farmers, fishermen and the hydroelectric company that operates the dams and distributes the water. The plan would set in motion one of the most ambitious efforts in U.S. history to restore the habitat of a federally protected species if it receives final approval by the parties in December, as expected.

The dams - Iron Gate, Copco 1, Copco 2 and J.C. Boyle - have blocked salmon migration for a century along the California-Oregon border and have been blamed for much of the historic decline of chinook and coho salmon and steelhead trout in the Klamath. Under the plan, the dams operated by the utility, PacificCorp, would be dismantled beginning in 2020.

The ultimate goal of the so-called Klamath Hydroelectric Settlement Agreement is to restore what has historically been the third-largest source of salmon in the lower 48 states, behind the Columbia and Sacramento rivers. Chinook once swam all the way up to Upper Klamath Lake in Oregon, providing crucial sustenance to American Indians, including the Yurok, Karuk, Klamath and Hoopa Valley tribes.

"This is the deal that we have all been working on for 10 years," said Steve Rothert, the California director of American Rivers, a national nonprofit river conservation group. "There were a lot of people who didn't think we could do this, and some groups that worked actively to prevent it. It's fantastic that we've reached this spot."

The groups involved in the negotiations agreed Tuesday to take the proposal to their various boards and commissions for approval and then have everybody sign the final document in December.

The project, which would cost an estimated $450 million, is then expected to go through nearly three years of study and cost analysis before it lands on the desk of Interior Secretary Ken Salazar in 2012. "This agreement marks the beginning of a new chapter for the Klamath River and for the communities whose health and way of life depend on it," Salazar said Tuesday in a written statement. "This agreement would establish an open, scientifically grounded process that will help me make a fully informed decision about whether dam removal is in the public interest."

Serious talk of removing the dams began in 2002 after a federally ordered change in water flow led to the death of 33,000 salmon in the river.

The effort picked up momentum over the past few years after devastating declines in the number of spawning salmon in both the Klamath and Sacramento river basins. The paltry number of fish forced regulators to ban virtually all ocean fishing of chinook salmon in California and Oregon over the past two years.

The four midsize dams were built along the Klamath's main stem starting in 1909, blocking off about 300 miles of salmon-spawning habitat. The dams warmed the river water, allowing destructive parasites and blooms of toxic, blue-green algae to contaminate the water. Water diversions to cities and for agriculture exacerbated the problem, according to fishery biologists.

The various tribes with rights to the river have been battling for years to get the dams removed. Fishermen and environmentalists rallied to their side, but PacifiCorp and farmers along the Upper Klamath Basin fought the effort and even sought to extend the hydropower lease.

Some agricultural groups still oppose the plan out of fear that it would limit irrigation and raise the cost of energy, and a few claim it is little more than a giveaway to environmental interests, but most of the stakeholders now at least support moving forward.

"I cannot adequately say how impressed I am by everyone's ability to put aside their differences," said Craig Tucker, spokesman for the Karuk Tribe. "There is a long history of not getting along, of fighting over water rights. Now we are optimistic."

PacifiCorp has pledged to raise $200 million of the cost of removing the dams by implementing a surcharge on its customers in California and Oregon, but the bulk of the money would come from Oregon.

Tearing down the dams is expected to cost less than making the improvements necessary to comply with the federal Clean Water Act and Fish and Wildlife Agency regulations, which would require, among other things, the construction of fish ladders and screens. The utility would have to get certification from both states under the Clean Water Act to continue operating the dams, a potentially difficult proposition given the algae problems.

"We've really looked at this as a business deal, and we believe it is in the best interests of our customers," said Dean Brockbank, vice president and general counsel for PacifiCorp. "The agreement we have now is a collaborative effort, and we believe it beats all of the alternatives."

California would raise another $250 million from voter-approved general obligation bonds.

Coming thursday: Decades after decimating salmon and spurring numerous lawsuits, Friant Dam will begin releasing more water into the San Joaquin River - California's second largest.